Bowditch Flashcards
Define Dead Reckoning
Determining a position by advancing a known position based on course and speed
Define Piloting navigation
Navigating in restricted waters with frequent and constant positions to nearby geographic and hydrographic features
What is a great circle?
A line of intersection of a sphere and a plane through its center. A great circle represents the shortest distance on a sphere.
What is a meridian?
Line of longitude - a great circle that passes through both poles
What is a parallel?
Line of attitude - a small circle (except equator, which is a great circle)
What is a Rhumb Line?
Measure of distance of navigation. A line from point A to B that crosses all meridians at the same angle
What are small scale charts used for?
Route and voyage planning
What are sailing charts?
The smallest scale charts, generally about 1:600,000 or smaller. Used for long range DR, voyage planning, etc
Where can you find descriptions and definitions of chart symbols?
Chart number 1
What is the difference between italicized and non-italicized fonts on a chart?
Non-italicized indicates that the feature is dry at high tide - it is not affected by the water level. Italicized features are either floating or underwater at high tide.
What feature on charts typically are shaded in blue tint?
Shoal water
What is a Sounding Datum?
A reference level that all depths are based off of charts
What is the Sounding Datum used for US and Puerto Rican Charts?
Mean Lower Low Water
What does a wreck circled by a dashed line indicate?
The wreck is less than 11 Fathoms
What color is a TSS on a chart?
Magenta
What is the difference between the List of Lights and the Light List?
List of Lights is for International waters, Light List is for the US
What is the Luminous Range of a light?
The distance at which a light can be seen under existing visibility conditions. It ignores the curvature of the earth, height of eye, height of the light, and background lighting
What is the Nominal Range of a light, and where is it listed?
The Nominal Range is the distance a light can be seen with 10 NM visibility range. It is listed in the Light List.
Where can you find detailed information about ports world wide?
The NIMA World Port Index
A closed drawbridge is marked by what color lights?
Red
What is an occulting light?
The duration of light is always GREATER than the duration of dark - it flashes OFF
What is a flashing light?
The duration of light is always LESS than the duration of dark - it flashes ON (Less than 50 flashes/minute)
What is an Isophase light?
Duration of light and dark are equal
What is a Quick Flashing Light?
A light for which a flash is regularly repeated at a rate between 50 to 80 flashes per minute.
What is a sector light?
Changes color based on the angle it is being viewed from - red usually means the ship is sailing into danger
What action should be taken if a light is not operating as prescribed?
It should be immediately reported to the nearest Coast Guard Station
What is IALA “A”?
Green buoys are on the right side when returning to port
What is IALA “B”?
Red Right Returning
What is a Cardinal Mark used for?
Points to the direction of safe water - for example, you should sail to the North of a North Cardinal Marked Buoy
How is a North Cardinal Buoy marked?
Two cones, both pointing up
How is a South Cardinal Buoy marked?
Two cones, both pointing down
How is a West Cardinal Buoy marked?
Two cones, apes touching (Looks like a wineglass - West = Wineglass)
How is an East Cardinal Buoy marked?
Two cones, bases touching
What is Variation?
Angular difference between magnetic and geographic meridians
Where is the amount of Variation found?
Pilot charts or on the compass rose on the chart
What is Deviation?
The amount of deflection of the ships magnetic compass from the magnetic meridian, caused by the ships magnetic signature
What is the sum of deviation and variation called?
Compass error
How much distance does 1 minute of latitude equal?
1 NM
What is Set and Drift?
Set is the direction being pushed by the current, Drift is the distance pushed
What must be highlighted on a chart prior to entering port?
The minimum depth contour
What is the formula to determine a ship’s minimum operating depth?
Minimum depth = Draft - Height of Tide + Safety Margin + Squat
What features should be circled and labeled on charts prior to entering port?
Navaids to be used
What three logs are required to be kept on the bridge while piloting?
Fathometer Log, Bearing Book, and Deck Log
How often should visual fixes be taken in restricted waters?
Not more than 3 minutes
What should be calculated at every fix while piloting in restricted waters?
Set and Drift
What is the hazard of anchoring in water that is too deep?
The anchor may drag
What is the preferred bottom type for anchoring?
Mud or sand
How much anchor chain should be let go?
5-7 times the depth of the water
How often should fixes be taken immediately after anchoring to determine if the anchor is holding or dragging?
Every three minutes for the first 30 minutes
If the anchor is holding, what is the maximum interval of fixes to be taken while at anchor?
No more than 30 minutes
What is a semi-diurnal tide?
2 high and 2 low tides per day
What is a diurnal tide?
1 high and 1 low tide per day
What is a spring tide?
When the sun, moon, and earth line up and results in greater range of tides
What is a neap tide?
When the sun is at a right angle to the moon, resulting in lower range of tides
What is a tidal datum?
Average tide level from which heights of tide and overhead clearances are measured
What direction do oceanic currents flow in?
CW in the northern Hemisphere, CCW in the southern
What is the difference between slack water and stand water?
Slack is no change in current, stand is no change in the tide
Direction and speed of the current are referred to as what?
Set is the direction, drift is the speed
What is the difference between an ECS and an ECDIS?
ECS is an electronic chart system, not designed to satisfy regulation for SOLAS - only an aid. An ECDIS does satisfy these requirements, and can be used as a chart replacement
Who is required to produce all Navy ECDIS-N charts, and in what format?
NIMA, in Vector format
What system is ECDIS-N contained in?
NAVSSI
What are three main functions of NAVSSI?
- Deliver navigation info to nav team members
- Weapons systems inputs
- Battlegroup planning
Who is responsible for establishing TSS’s?
The International Maritime Organization (IMO)
What is the international signal to tell a vessel they are not operating IAW the TSS?
YG
What band does AIS use?
VHF
What is an early indication of a tropical cyclone?
Long swells decreasing from 8 per minute to 4 per minute
What type of clouds precede a cyclone?
Cirrus
How can you tell the direction of the center of a cyclone?
Swells come from the center, and cirrus clouds converge at the center
